1. Field of the Invention
The present invention relates to a zoom lens drive mechanism and, in particular, to a zoom lens drive mechanism which is capable of zoom driving and focus driving zoom lenses including a front group of lenses and a rear group of lenses.
2. Description of the Related Art
Generally, a zoom lens is composed of a group of focus lenses, a group of varying lenses, a group of compensator lenses and a group of master lenses.
Therefore, an image of an object to pass through the above-mentioned zoom lens is first formed by the focus lens group and the image is then altered in magnification before it is formed. Further, after the image point movement of the formed image, of which magnification has been altered by the above-mentioned varying lens group, is corrected by the compensator lens group, the formed image is formed on the surface of an image pickup device as the object image by the master lens group which does not participate in the zooming but remains stationary.
In such zoom lens, the focal point thereof can be adjusted by rotating, for example, a focus ring to thereby move the focus lens group in the optical axis direction thereof, and the magnification thereof can be changed without moving the focal point thereof by rotating a zoom ring to thereby move the varying and compensator lens groups in the optical axis direction thereof with a given relation between the two lens groups.
Also, due to the fact that the above-mentioned zoom lens is composed of the four lens groups, the movement of the focus lens group for adjustment of the focus and the movement of the varying and compensator lens groups in zooming do not interfere with each other. On the other hand, when a zoom lens is composed of two lens groups, that is, a front lens group and a rear lens group, in order to adjust its focal point, only the front lens group must be moved, and, in zooming, the front and rear lens groups must be moved simultaneously. For this reason, it has been difficult to realize a simple structure which is free from the interference between the two kinds of movements.